1. Field of the Invention
The present invention relates to an electroconductive member used in an electrophotographic copying machine, printer or the like, and an image forming apparatus using the same.
2. Description of Related Art
In an image forming apparatus using an electrophotographic manner, uniform electric charges are formed (electrification) on the surface of an electrostatic latent image carrier (photoreceptor), and an electrostatic latent image is formed using a laser with modulated image signals. Thereafter, the electrostatic latent image is developed with electrified toner to form a toner image. The toner image is electrostatically transferred, through an intermediate transfer member or directly, onto a recording medium, whereby a desired transferred image can be obtained.
In the transferring manner using the intermediate transfer member, a semiconductive endless belt (semiconductive belt) is adopted as the intermediate transfer member. This semiconductive belt is generally made of an elastic material from the viewpoint of easy control of the driving of the belt, and the other viewpoints. In general, a vulcanized rubber as follows is used: ethylene-propylene-diene rubber (EPDM), urethane rubber, epichlorohydrin rubber.
For example, Japanese Published Unexamined Patent Application No. Hei 2-264277 suggests the use of a belt wherein a polyethylene film is laminated on an EPDM rubber having a volume resistivity of 1015 to 1016 xcexa9cm. Furthermore, Japanese Published Unexamined Patent Application No. Sho 63-83764 suggests a semiconductive belt or the like wherein an elastic body is used as a material having a volume resistivity of about 1010 to 1013 xcexa9cm.
Since the semiconductive belt is made of an elastic body having high elasticity, the belt has a higher tensile strength than elastomers. The transferring semiconductive belt for forming an image is required to have given paper-passing durability as well as a high tensile strength. About this paper-passing durability, a good performance is obtained by setting the thickness of the belt to a given thickness.
In the case in which the following is used in order to obtain such a high tensile strength and given paper-passing durability: for example, the transferring carrying belt described in the Japanese Published Unexamined Patent Application No. Hei 2-264277, having a volume resistivity of 1015 to 1016 xcexa9cm, or the transferring carrying belt described in the Japanese Published Unexamined Patent Application No. Sho 63-83764, having a volume resistivity of about 1010 to 1013 xcexa9cm, there arises a problem that an electric field necessary for the transfer becomes large so that a heavy burden is imposed on a power source for applying voltage to the belt.
Since the transferring carrying belt holds a transferring material (recording medium) through electrostatic absorption power, discharge of electricity may be generated when the transferring material is separated from the belt. In this case, a transfer image on the surface of the transferring material may be disturbed. This discharge is easily generated particularly under environment of a low temperature and low humidity. However, in the case in which the abovementioned semiconductive belt having a high volume resistivity is used as the transferring carrying belt, a high voltage is necessary for holding the transferring material by means of the belt; therefore, discharge of electricity is easily generated. This discharge phenomenon causes some parts of toner on the surface of the transferring material to reverse polarity. Thus, transfer defects are generated so that image defects called voids (white omissions, or drop-outs) are caused in some parts of the transferring material surface. Thus, the transfer image is easily disturbed to result in a problem that a good image quality is not easily obtained.
In the case in which the volume resistivity of the transferring carrying belt is less than 102 xcexa9cm, electric charges flow easily, thereby resulting in a problem that the transferring material cannot be held through electrostatic absorption power.
Japanese Published Unexamined Patent Application No. Hei 8-185068 suggests, as a transferring carrying belt, a belt wherein the surface of an elastic body having a volume resistivity of 109 xcexa9cm or less, such as chloroprene, is coated with a nylon resin or an urethane resin. In the case in which the surface layer of the chloroprene is coated with the nylon resin, the surface coat layer cannot follow deformation of the transferring carrying belt at a curvature portion, where the belt passes through a roll-shaped support, since the coat layer is hard. Thus, a crack may be generated in the surface layer. In the case of the urethane resin coat, the coat layer has flexibility not to cause a problem of the generation of a crack on the coat layer surface as described above. However, this belt has a problem that toner adheres easily to the surface so that the surface easily gets dirty.
In the case in which an elastic body such as chloroprene in which carbon black or the like is dispersed is used for the transferring carrying belt, a desired stable resistance value can hardly be obtained even if ordinary conductive carbon black is added to ordinary rubber material. This is because a semiconductive resistance range having a resistivity of about 109 xcexa9cm is a range wherein resistivity is not easily controlled. As a result, it is difficult that variation in the resistance of the belt using the abovementioned elastic body is stably set in such a manner that the common logarithm of the volume resistance thereof is within one figure (digit). In the case in which in-plane variation in the resistance is one figure or more, transferring voltage cannot be uniformly applied. Therefore, a problem arises that image quality after transfer is not stable.
In order that the semiconductive belt holds the transferring material and a toner image is transferred onto the transferring material, a transferring voltage of 1 to 5 kV is applied. This applied voltage causes a change in the resistance of the belt material, resulting in a problem that a difference in the resistance value of the belt is generated between the region where the transferring material is present and the region where it is not present.
To overcome a change over time in the resistance value of the abovementioned belt material and unevenness of the belt resistance value, Japanese Published Unexamined Patent Application No. Hei 8-292648 suggests a transferring carrying belt formed of three layers wherein the volume resistivity of the first layer (surface layer) is set within the range of 1xc3x971010 to 1xc3x971016 xcexa9cm; a rubber layer using the conductivity of a polymer itself, the volume resistivity range thereof being from 1xc3x97107 to 1xc3x971010 xcexa9cm, is used as the second layer (intermediate layer); and the volume resistivity of the third layer (base layer) is set within the range of 1xc3x971010 to 1xc3x971016 xcexa9cm. This publication states that the unevenness of the resistance value can be improved by the rubber layer using the conductivity of the polymer itself, which is the second layer (intermediate layer). However, in the case of the laminated belt, the resistance value thereof is controlled by the layer having a high resistance value. Thus, the unevenness of the resistance value is not sufficiently overcome.
Japanese Published Unexamined Patent Application No. Hei 9-179414 suggests a rubber material made of chloroprene rubber and EPDM (ethylene propylene diene monomer) as a countermeasure against the change over time in the resistance of the belt material. However, this suggestion is insufficient for overcoming this change over time and the unevenness of the belt resistance.
Furthermore, Japanese Published Unexamined Patent Application No. 7-271204 suggests the use of an ion-conductive type rubber material made of a rubber material having an intense polarity, such as hydrin rubber, as a countermeasure against the change over time in the resistance value of the belt material and the unevenness of the belt resistance value. In the case of using an electroconductive type rubber material using a conductive agent such as carbon black, a problem of a change in the resistance value does not arise between a high temperature with high humidity and a low temperature and low humidity. However, the ion-conductive type rubber material has a problem that the resistance value thereof changes by 1.5 figure or more between a high temperature and high humidity and a low temperature and low humidity.
In the abovementioned image forming apparatus using electrophotography, a contact charging manner using a charging member is adopted as the abovementioned charging processing manner. An charging roll is the most popular member as the charging member. It is known that the mechanism of electrification onto the surface of a photoreceptor (electrostatic latent image carrier) by means of this charging roll is based on electric discharge according to Paschen""s law in minute spaces between the charging roll and the photoreceptor. Since the contact type charging roll contacts the photoreceptor made of a metal substrate at a given pressing force and contact-rotates with rotation of the photoreceptor, a floating space is generated at a small hollow in the roll surface between the roll and the photoreceptor in the case in which the charging roll does not have sufficient flexibility. Thus, the abovementioned minute spaces are scattered so that electrification poorness is generated.
Therefore, in the charging roll, the generation of the floating space is prevented by depositing a conductive elastic layer on the surface of the conductive support (substrate). For this conductive elastic layer, a vulcanized rubber material as follows is generally used: the abovementioned ethylene-propylene-diene rubber (EPDM), urethane rubber, silicone rubber, or epichlorohydrin rubber.
In the conductive elastic layer of the charging roll, carbon black or the like is used as a conductive agent as described above. Therefore, if the resistance value thereof is set within a semiconductive range, variation in the resistance value becomes large, causing a problem that image defects such as electrification poorness are partially generated.
Incidentally, worldwide environment protection activities have been highlighted in recent years. For enterprises, activities in which importance is attached to environment, such as a cutback in energy consumption in a production process and a cutback in waste, have been demanded.
However, about the rubber materials to be vulcanized and used in the abovementioned belt or roll, energy is consumed in a vulcanizing step in the production thereof. Furthermore, once the material is vulcanized, recycle based on re-shaping thereof is impossible. Therefore, from the viewpoint of environment protection, these materials are very unfavorable.
Thus, it is considered that a thermoplastic elastomer material is used as the material of the belt or the roll instead of the vulcanized material. Since the thermoplastic elastomer can be shaped in the same way as in the case of thermoplastic resins, the elastomer has advantages for environment protection, such as omission of the vulcanizing step and adaptability for recycle. The thermoplastic elastomer can be worked more speedily with a shaping machine for thermoplastic resins than crosslinking elastomer. The thermoplastic elastomer requires only a short shaping cycle and requires no vulcanizing step. That is, the thermoplastic elastomer is an energy-saving, labor-saving and time-saving material and can realize a simple production process. Moreover, scraps thereof can easily be recycled since products from the elastomer have not been crosslinked.
However, in the case in which this thermoplastic elastomer is used for a semiconductive belt or the like, deformation is easily generated on the basis of the intrinsic stress strain of the material, as described above. Particularly in the case of a belt, the belt follows the curvature of a supporting roll on which the belt is stretched so as to deform easily when the running of the belt is stopped for a long time. Thus, it may be impossible that the belt adsorbs a transferring material electrostatically and carries the material stably. Furthermore, in the case in which an electroconductive agent such as carbon black is used, if the resistance value is set within a semiconductive range (about 106 to 1012 xcexa9m), variation in the resistance value is large. Thus, image defects such as partial transfer poorness are generated. The image defects are caused by the fact that the electroconductive agent is not easily dispersed uniformly in the thermoplastic elastomer to generate poor dispersion.
In the case in which such a material is used for a charging member whose resistance value is set within the semiconductive range, image defects such as partial electrification poorness are generated. When the conductive agent (carbon black) is dispersed as it is into a thermoplastic elastomer, the hardness of the conductive elastic layer itself rises, causing problems that electrification poorness is generated by poor contact thereof with a photoreceptor.
As a semiconductive thermoplastic elastomer, an elastomer in which carbon black is not dispersed but an ion conductive agent is dispersed is known. In this type of thermoplastic elastomer, variation in resistance value is smaller in the same manner as in the case of the crosslinking rubber than in the elastomer in which carbon black is dispersed. However, when the thermoplastic elastomer in which the ion conductive agent is dispersed is used, the following problems may be generated: the dependency of the resistance upon environment and a change in the resistance by continuous sending of an electric current are generated; and this ion conductive agent bleeds to contaminate the surface of a photoreceptor surface. This phenomenon is remarkable when the blend amount of the ion conductive agent is made large.
As a unit that solves these problems, it is considered that a protective layer having a barrier function is deposited on the surface of the conductive elastic layer. However, this protective layer is required to be thin and homogenous and have a good surface property in order not to damage the function of the transferring carrying belt. In a charging roll or the like on which such a protective layer is formed by such a unit, an ion conductive agent also bleeds from its semiconductive elastomer layer to the surface of the protective layer so that the surface of a photosensitive roll may be contaminated.
In view of the abovementioned circumstances, the present invention provides an electroconductive member which includes an electroconductive composition using a thermoplastic elastomer material having advantages such as reduction in energy of a production process thereof and capability of being recycled, and which makes it possible to prevent a change in resistance by sending an electric current, improve uniformity of electric resistance, and reduce the dependency on an electric field and a resistance-change by environment. The present invention also provides an image forming apparatus using the abovementioned electroconductive member.
An aspect of the present invention provides an electroconductive member including an electroconductive resin composition having an epoxidized diene block copolymer, a thermoplastic elastomer other than the epoxidized diene block copolymer or a thermoplastic resin and a conductive agent.
Another aspect of the present invention provides an electroconductive member, wherein the electroconductive resin composition includes the epoxidized diene block copolymer, the thermoplastic elastomer other than the epoxidized diene block copolymer, and the conductive agent, the member being a semiconductive belt including the electroconductive resin composition.
Another aspect of the present invention provides an electroconductive member, wherein the electroconductive resin composition includes the epoxidized diene block copolymer, the thermoplastic elastomer other than the epoxidized diene block copolymer, and the conductive agent, the member being an electroconductive roll, wherein an electroconductive elastic layer containing the electroconductive resin composition is formed on a surface of a substrate.
Another aspect of the present invention provides an image forming apparatus wherein the electroconductive member is the abovementioned semiconductive belt and used as a transfer material carrying belt.
Another aspect of the present invention provides an image forming apparatus wherein the electroconductive member is the abovementioned semiconductive belt and used as an intermediate transfer member.
Another aspect of the present invention provides an image forming apparatus wherein the electroconductive member is the abovementioned electroconductive roll and used as a charging unit.
Another aspect of the present invention provides an image forming apparatus wherein the electroconductive member is the abovementioned electroconductive roll and used as an intermediate transfer member.